The present invention relates to a process for removing friable material from a surface. The invention is particularly useful for removing asbestos from buildings or other structures, although it may also be employed for removing other crumbly or loosely attached coatings such as flaking paint or rust, barnacles, and so forth.
Asbestos is a fiberous mineral material having a number of uses which have long been recognized. For example the fibers may be spun to provide an insulating cloth, or used as a filler in gaskets or tiles. At one time asbestos was used extensively in the construction industry to provide heat-resistant barriers and fire-proofing. One conventional technique was to mix the asbestos fibers with cementing material and spray the mixture on a surface to be protected, whereupon the mixture would harden to a fleecy coating of perhaps two inches thick. Such coatings were used even on concrete or metal surfaces to provide protection from the intense heat which might occur during a fire.
Unfortunately the desirable properties of asbestos were exploited in the construction industry long before its undesirable properties were appreciated. It has been found that asbestos fibers contribute to severe medical problems such as asbestosis and lung cancer. Because of this an industry has developed to remove asbestos coatings from habitable structures. A conventional removal technique will be described with reference to FIGS. 1 and 2.
In FIG. 1, an asbestos coating 10 is to be removed from ceiling 12. The area is first prepared to protect uncoated surfaces from contamination by air-borne asbestos fibers. To provide such protection FIG. 1 illustrates a plastic sheet 14 which is taped to a wall (not illustrated) adjacent ceiling 12. Thereafter the coating 10 is sprayed with a solution (such as water plus a surfactant, a mixture which is known as "amended water") to limit contamination, and is periodically re-sprayed throughout the removal process. The amended water reduces asbestos dust. A workman 16 wears a protective garment which is provided with a hood 18. Workman 16 wears a respirator (not illustrated) which is supplied with air by a breathing apparatus 20 worn on the workman's belt 22. Supported by scaffolding 24, workman 16 employs a scraper 26 to strip asbestos coating 10, which falls away in an asbestos stream 28 and is subsequently discarded. It will be apparent that a small scraper such as a putty knife, not illustrated, may be used to scrape regions too small for the scraper 26 shown in FIG. 1.
FIG. 1 illustrates a region 30 which has been scraped and a region 32 which is awaiting scraping. Although workman 16 attempts to scrap region 30 down to the bare concrete of ceiling 12, as a practical matter streaks or other regions of asbestos residue 34 almost invariably remain in region 30 after the scraping step. In the present application the step of removing patches of residue 34 will be deemed the "residue removal" step.
FIG. 2 illustrates the conventional residue removal step. In FIG. 2, ceiling 12 is supported by an I-beam 36, and patches of asbestos residue 34 remain after the scraping step has been completed. Conventionally these patches 34 are removed using an elongated wire brush 38. After the residue removal step the cleaned surfaces may be sprayed or painted with an encapsulating material (not illustrated) to trap any asbestos fibers that may remain.
In order to protect his hands from accidents during the conventional residue removal step, a workman typically uses an end row 42 of bristles to remove residue from a corner region adjacent an obstruction such as I-beam 36. Such a corner region is illustrated at 44. The use of end row 42 reduces the risk that the workman's hand might accidentally scrap against I-beam 36 during vigorous brushing, but as a result the end row 42 of bristles is the first to become bent and worn out. While the brush 38 might still be useful for large flat expanses away from obstructions, in actual practice there is a strong tendency for workmen to discard a brush 38 after its end-rows have become worn.
Another factor limiting the life of brush 38 is the wet environment in which it is used. This causes the bristles to rust and the wooden handle 40 to swell, so that the bristles tend to fall out. The net result is that a brush 38 may still have satisfactory end rows 42 of bristles when it is put away at the conclusion of work on one day, but nevertheless be discarded in favor of a new brush when the work resumes on the following day or on a Monday after a weekend.
Although the cost of brushes 38 themselves is significant, the major financial consideration in the asbestos removal industry is the cost of labor. A wire brush 38 is relatively heavy, particularly when water logged, and in view of the awkward physical stance that is frequently necessary this weight can be quite tiring. Consequently workmen generally proceed at a relatively modest pace in order to avoid exhaustion. Furthermore workmen have a tendency to brush back and forth rather than to sweep from side to side, which is more tiring and might result in an injury to the workman's hand if the hand and brush accidentally roll during a sweep. This tendency to favor brushing back and forth also limits productivity. Productivity is further reduced if the surface is a curved one, since a brush rides tangent to the curve and hence only a portion of the bristles engage the surface.
There are safety considerations in addition to these economic factors. While it would be inappropriate to deem a wire brush a safety hazard, it is nevertheless true that a wire brush may imperil a workman if he accidentally brushes against a "live" electrical fixture or wire. Furthermore the wire brushing of asbestos needlessly fragments the fibers into smaller fibers an propels them into the air. Obviously adding airborne asbestos to the environment in this way is undesirable. In addition, wire brushing may contribute to eye injuries if particles (either asbestos or rust, scale, paint chips, etc.) are "sprung" by the bristles into the workman's face. The projection of particles by a brush can also spread asbestos contamination to previously cleaned or otherwise uncontaminated areas. Finally, a wire brush may lead to disaster if it strikes sparks when used in an explosive environment.
What might be called the "bag method," not illustrated in the accompanying drawings, may be used to remove asbestos from pipes and valves. In this method plastic sheets to protect uncoated areas (e.g., sheet 14 in FIG. 1) may be omitted since the asbestos is always contained within a special bag of transparent plastic. Removal tools are placed in the bag, which is then sealed around the pipe so that a segment of the pipe is disposed within the bag. Reaching through long gloves which are provided in the bag wall, a workman uses the tools to remove the asbestos coating and to clean residue from the pipe. The asbestos falls to the bottom of the bag, which is then tied off and cut away from the remaining portion of the bag.
When the bag method is used care must be taken not to breach the integrity off the plastic bag, since a puncture would release asbestos fibers. Brushes, and particularly wire brushes, must be used with due caution to avoid such punctures.
Although wire brushes are employed extensively in the industry some authorities would prefer to avoid their use. For example the Division of Environmental Disease Control, of the Maryland Department of Health and Mental Hygiene, has published a "Recommended Contract Specifications for Asbestos Abatement Projects" which recommends that brushes have nylon or fiber bristles rather than metal bristles. Some of the problems discussed above would be ameliorated by using nylon or fiber brushes instead of wire brushes, but it will be apparent that most of the problems would remain.